Field of the Invention and Related Art Statement
This invention relates to a method of detecting flaws or defects formed in a surface of a rotating member such as a ball or a cylindrical roller of a bearing with the aid of an ultrasonic wave, and an apparatus for carrying out such an ultrasonic flaw detecting method.
Flaws formed in a surface or bulk of a rotating bearing member have been tested or detected by an X-ray inspection technique, a fluorescent penetration inspection technique or by observing with a microscope or the naked eye.
However, these known techniques have some disadvantages in that a great deal of time is needed for testing, and it is impossible to detect fine flaws in the surface of the rotating bearing member. Especially, defects formed in the vicinity of the surface of the bearing member could not be effectively detected by means of conventional testing methods.
There has been also proposed an immersion type detection method which can detect flaws formed in the vicinity of an inner surface of a cylindrical member like a thin steel tube. Such a method has been described in a Japanese publication, "Ultrasonic Flaw Testing Method", edited by Steel Manufacture the 19th Committee of the Japan Society for the Promotion of Science, published by Nikkan Kogyo Shinbun-sha on July 30, 1974, pp. 491.about.493.
FIG. 1A is a schematic view showing the known immersion type ultrasonic flaw testing apparatus and FIG. 1B illustrates an echo signal appearing therein. In this method, a steel tube 1 to be tested is immersed in an ultrasonic wave propagating medium M such as water, and an ultrasonic wave is projected from a probe 2 toward the tube 1 by supplying an output signal of an oscillator 3 to the probe. The probe 2 is arranged off-axis with respect to the tube 1. That is to say, a center axis X of the ultrasonic wave is displaced from a vertical center axis Y of the steel tube 1 by such a distance that the ultrasonic wave penetrates into the tube and arrives at the inner surface 1a of the tube, and echoes reflected from the vicinity of the inner surface of the steel tube are received by the probe 2 as shown in FIG. 1B. Then an echo signal generated by the probe 2 is amplified by an amplifier 4 and then is displayed on a Brawn tube 5. At the same time, a range within which the flaws are to be detected is determined by a signal gate 6. The range thus determined is also displayed on the Brawn tube 5 through a detection range display circuit 7 as shown by a window W in FIG. 1B. In FIG. 1B, T denotes a transmitted pulse, S an echo signal reflected from the outer surface of tube and F represents an echo signal reflected from the bulk and inner surface of the tube. The echo signal selectively passed through the signal gate 6 is processed by a signal converter 8. When a flaw is detected within the selected range, an alarm is generated by an alarm 9, and the output signal from the signal converter is recorded by a recording device 11 via an amplifier 10.
By rotating the steel tube 1 in a direction shown by an arrow and moving the probe 1 in the longitudinal direction of the steel tube, any flaw formed in the vicinity of the inner surface 1a of the steel tube 1 can be tested continuously.
However, this known immersion type flaw detecting apparatus is designed to selectively detect flaws formed in the inner surface and the vicinity thereof of a steel tube, and the center axis X of the ultrasonic wave, i.e. the center axis of the probe 2 is laterally shifted from the vertical center axis Y of the steel tube 1 by such an amount that the ultrasonic wave can propagate efficiently within the tube up to the inner surface 1a of tube. Therefore, this known apparatus could not be utilized to detect flaws formed in an outer surface of tube or in the vicinity thereof. Particularly, this known apparatus is not suitable for detecting flaws formed in the surface of a rotating bearing member made of ceramics. In the rotating bearing member, defects formed in the vicinity of the outer surface thereof greatly affect the performance of the bearing.